Guan Sheng Optical is one of the world's largest manufacturers of telescopes and astronomy accessories.
The GSO Ritchey-Chrétien telescopesare excellent astrographs with solid build quality and precisely-figuredoptical surfaces. The concave hyperbolic primary and convex secondary mirrors deliver excellent correction across the field. The low thermal expansion quartz mirrors have a surface flatness of 1/12th wave or better and have highly reflective dieletric coatings ensuring 99% reflectivity.
The Ritchey-Chrétien telescope is the most popular optical design used by professional astronomers and astroimagers all over the world. The Hubble Space Telescope itself uses the RC configuration.